Most common cereal grains contain cells called aleurone cells that occur as the most external layer of the endosperm. Aleurone cells are generally oil and protein-rich and secrete enzymes allowing the mobilization of endosperm reserves during seed germination. Barley, oats, and some varieties of rice have been reported to have 2 to 4 layers of aleurone cells (Sawicki et al., 1952, and Hoshikawa et al, 1967). Maize commonly has only a single layer making up only 2% or less of the weight of the kernel (Hinton et al, 1953). A South American race of maize, Coroico, has been found to contain from 2 to 6 layers of aleurone cells (Wolf et al, 1972). This characteristic has been referred to as the Mal (multiple aleurone) phenotype by Welch et al, 1993.
When compared to grains having only a single layer of aleurone cells, varieties having multiple aleurone cell layers contain increased amounts of minerals (Welch et al., 1993) and protein (Wolf, ibid). However, the Mal phenotype is inherited as a partially dominant trait and is highly variable in the Coroico line. To date, a reliable, multiple aleurone trait has not been available in maize or other cereal crops that could be used in a breeding program to take advantage of the unique characteristics of aleurone cells.
Thus, a transgenic or breeding approach that alters the number of aleurone cells in a grain crop as well as the characteristics of the aleurone cells would be highly desirable.